Update Linux desktop integration instructions

Your Godot version:
v4.2.1

Issue description:
The Linux desktop integration instructions could use two changes (IMO):

1. The "Rename and move the Godot binary to a location present in your PATH environment variable" section doesn't mention $HOME/.local/bin/ as an option to place the Godot binary. This location doesn't require administrator privileges, so might be a better option for some users. Certainly worth a mention in any case.
2. Mention how to get the icon to show up. I'm on KDE, and in the main application menu Godot doesn't have an icon (after following the linked instructions). Similar to the "Save this .desktop file to $HOME/.local/share/applications/" section, I think explaining where to download and save the Godot icon would be useful too.

URL to the documentation page (if already existing):
https://docs.godotengine.org/en/stable/about/faq.html#linux

For part 2 above, the step seems to be saving https://github.com/godotengine/godot/blob/master/icon.svg as godot.svg in $HOME/.local/share/icons/.

[Calinou]

1. The "Rename and move the Godot binary to a location present in your PATH environment variable" section doesn't mention $HOME/.local/bin/ as an option to place the Godot binary. This location doesn't require administrator privileges, so might be a better option for some users. Certainly worth a mention in any case.

This location isn't always present in PATH, so you have to add it in /etc/environment (which require administrator privileges to be modified) if you want the binary to be reliably available in PATH. Adding it to your ~/.bashrc won't suffice if you're running apps from a desktop environment, as it doesn't source environment variables from your ~/.bashrc.